System to improve after-treatment regeneration

ABSTRACT

Exemplary methods, devices, and/or systems are suitable for regenerating a plurality of after-treatment units. An exemplary method includes selecting less than all of a plurality of after-treatment units and adjusting air to fuel ratio for less than all of a plurality of combustion chambers of an engine to thereby cause the selected after-treatment units to receive exhaust having hydrocarbon and oxygen concentrations that favor regeneration of the selected after-treatment units. Other exemplary methods, devices and/or systems are also disclosed.

RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/362,619, filed Mar. 7, 2002, entitled “System toImprove After-treatment Regeneration”.

TECHNICAL FIELD

[0002] This invention relates generally to methods, devices, and/orsystems for improving after-treatment regeneration for an internalcombustion engine.

BACKGROUND

[0003] As diesel engine emissions legislation becomes more stringent, anumber of new technologies are under investigation and fall in thegeneral category of “after-treatment”. These technologies include, butare not limited to diesel particulate filters, oxidation catalysts, andNOx traps. Most after-treatment filters, catalysts, traps, etc., whichmay be referred to as after-treatment units, require some sort of“regeneration” to refresh their emissions reducing capacity.

[0004] Regeneration techniques vary from technology to technology, butusually involve changing either the temperature or equivalence ratio(e.g., air to fuel ratio relative to a stoichiometric ratio) of theexhaust. For example, a diesel particulate filter typically requiresquite high temperatures to burn off particulates trapped in the filter.As another example consider the NOx trap, which typically requiresregeneration several times per minute. During regeneration of a NOxafter-treatment unit, the air to fuel ratio, which normally runs leantypically at approximately 19:1 to approximately 27:1 at full load andmuch higher at part load, is reduced to achieve rich combustion (e.g.,an air to fuel ratio at or below approximately 14:1). However, variousproblems may be encountered when operating at such low air to fuelratios. For example, depending on combustion temperature, unsatisfactorylevel of smoke may be generated at low air to fuel ratios.

[0005] Traditionally, an after-treatment unit is placed in an engineexhaust stream after an exhaust turbine. During regeneration, the engineis operated in a significantly different thermodynamic regime thanduring normal operation. The thermodynamic regime suited to regenerationmay have a substantial impact on engine operation. For example, such athermodynamic regime may confound control of torque to maintain acommanded level by an operator or control of an air management systemthat includes a turbocharger (e.g., to maintain a smooth airflow). Inparticular, during a typical 2 to 4 second NOx unit regeneration, areduction in mass flow occurs across the entire engine, typically by afactor of approximately two. Such a reduction in mass flow results inunsatisfactory conditions for turbocharger operation. For example,during regeneration, a significant variation in turbine speed may occur,which may cause undesirable pressure gradients at the inlet manifoldthat can result in further outlet manifold pressure disturbances.

[0006] Overall, after-treatment regeneration presents tremendouschallenges in engine management control and system design whereacceptable emissions and operator satisfaction are imperative. Hence, aneed exists for new or improved methods, devices and/or systems forafter-treatment regeneration. Various exemplary methods, devices and/orsystems presented below meet this need and/or other needs.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] A more complete understanding of the various exemplary methods,devices and/or systems described herein, and equivalents thereof, may behad by reference to the following detailed description when taken inconjunction with the accompanying drawings wherein:

[0008]FIG. 1 is a simplified approximate diagram illustrating anexemplary system that includes a turbocharger and an internal combustionengine.

[0009]FIG. 2 is a simplified approximate diagram illustrating anexemplary system that includes a one-to-one correspondence betweenafter-treatment units and combustion chambers and regulators to regulateat least EGR pressure and/or flow to individual combustion chambers.

[0010]FIG. 3 is a simplified approximate diagram illustrating anexemplary system that includes a one-to-one correspondence betweenafter-treatment units and combustion chambers, regulators to regulate atleast EGR pressure and/or flow to individual combustion chambers andregulators to regulate pressure and/or flow to each of theafter-treatment units.

[0011]FIG. 4 is a simplified approximate diagram illustrating anexemplary system that includes a one-to-one correspondence betweenafter-treatment units and combustion chambers, regulators to regulate atleast intake air pressure and/or flow to individual combustion chambersand regulators to regulate pressure and/or flow to each of theafter-treatment units.

[0012]FIG. 5 is a block diagram illustrating an exemplary methodsuitable for regeneration of an after-treatment unit.

[0013]FIG. 6 is a plot showing exemplary combustion trends.

[0014]FIG. 7 is an exemplary plot of NOx and after-treatment unittemperature versus time for an exemplary method of regeneration.

[0015]FIG. 8 is an exemplary plot of power versus time for an exemplarymethod of regeneration.

[0016]FIG. 9 is an exemplary plot of power versus time for an exemplarymethod of regeneration with power compensation.

[0017]FIG. 10 is a block diagram of an exemplary method suitable forregeneration of one or more after-treatment units.

[0018]FIG. 11 is a block diagram illustrating an exemplary controllerfor controlling regeneration and/or other engine operations.

DETAILED DESCRIPTION

[0019] Turning to the drawings, wherein like reference numeralsgenerally refer to like elements, various exemplary methods areillustrated as being implemented in a suitable control and/or computingenvironment. Although not required, various exemplary methods aredescribed in the general context of computer-executable instructions,such as program modules, being executed by a computer and/or othercomputing device. Generally, program modules include routines, programs,objects, components, data structures, etc. that perform particular tasksor implement particular abstract data types.

[0020] In some diagrams herein, various algorithmic acts are summarizedin individual “blocks”. Such blocks describe specific actions ordecisions that are made or carried out as a process proceeds. Where amicrocontroller (or equivalent) is employed, the flow charts presentedherein provide a basis for a “control program” or software/firmware thatmay be used by such a microcontroller (or equivalent) to effectuate thedesired control. As such, the processes are implemented asmachine-readable instructions storable in memory that, when executed bya processor, perform the various acts illustrated as blocks. Inaddition, various diagrams include individual “blocks” or “modules” thatare optionally structural elements of a device and/or a system. Forexample, a “controller block” optionally includes a controller as astructural element, an “actuator block” optionally includes an actuatoras a structural element, a “turbocharger block” optionally includes aturbocharger as a structural element, etc. In various blocks, structureand function are implied. For example, a controller block optionallyincludes a controller (e.g., a structure) for controlling an enginerelated parameter (e.g., a function).

[0021] Those skilled in the art may readily write such a control programbased on the flow charts and other descriptions presented herein. It isto be understood and appreciated that the subject matter describedherein includes not only devices and/or systems when programmed toperform the acts described below, but the software that is configured toprogram the microcontrollers and, additionally, any and allcomputer-readable media on which such software might be embodied.Examples of such computer-readable media include, without limitation,floppy disks, hard disks, CDs, RAM, ROM, flash memory and the like.

[0022]FIG. 1 shows an exemplary system 100 that includes an exemplaryinternal combustion engine 110 and an exemplary turbocharger 120. Theinternal combustion engine 110 includes an engine block 118 housing oneor more combustion chambers (e.g., cylinders, etc.) that operativelydrive a shaft 112. As shown in FIG. 1, an intake manifold 114 provides aflow path for intake air to the engine block 118 while an exhaustmanifold 116 provides a flow path for exhaust from the engine block 118.

[0023] The exemplary turbocharger 120 acts to extract energy from theexhaust and to use this energy to boost intake charge pressure (e.g.,pressure of intake air, etc.). As shown in FIG. 1, the turbocharger 120includes a shaft 122 having a compressor 124, a turbine 126, an intake134, and an exhaust outlet 136. Exhaust from the engine 110 diverted tothe turbine 126 causes the shaft 122 to rotate, which, in turn, rotatesthe compressor 124. When rotating, the compressor 124 energizes intakeair to produces a “boost” in intake air pressure (e.g., force per unitarea or energy per unit volume), which is commonly referred to as “boostpressure.” In this manner, a turbocharger may help to provide a largermass of intake air (e.g., typically mixed with a carbon-based and/orhydrogen-based fuel) to the engine, which translates to greater engineoutput during combustion.

[0024] An exhaust turbine or turbocharger optionally includes a variablegeometry mechanism or other mechanism to control flow of exhaust to theexhaust turbine. Commercially available variable geometry turbochargers(VGTs) include, but are not limited to, the GARRETT® VNT™ and AVNT™turbochargers, which use multiple adjustable vanes to control the flowof exhaust through a nozzle and across a turbine. Further, the exemplarysystem 100 may include a turbocharger or compressor having an associatedelectric motor and/or generator and associated power electronics capableof accelerating and/or decelerating a shaft (e.g., compressor shaft,turbine shaft, etc.). Power electronics may operate on DC power andgenerates an AC signal, or vice-versa, to drive a motor and/orgenerator.

[0025] The exemplary system further includes an after-treatment unit 138positioned in the exhaust stream after the turbine 126. Theafter-treatment unit 138 is optionally a diesel particulate filter,oxidation catalyst, a NOx trap or some other type of after-treatmentunit. Further, the after-treatment unit 138 may include one or moresubunits or combination units capable of performing any of a variety ofafter-treatments. Conventional engine systems generally have one or moreafter-treatment units positioned in an exhaust stream after aturbocharger (e.g., after an exhaust turbine). As described herein, anafter-treatment unit may be an individual unit or a block unit having aplurality of separate flow paths (e.g., subunits) wherein, for example,a flow path or subunit may be configured to receive exhaust from onlypart of an engine's exhaust stream (e.g., from a particular combustionchamber, etc.).

[0026] In general, after-treatment regeneration of any particularafter-treatment unit is facilitated where a unit receives only part ofan engine's exhaust stream. Hence, as described herein various exemplarymethods, devices and/or systems include or operate one or moreafter-treatment units in an exhaust stream prior to an exhaust turbine.Further, various exemplary methods, devices and/or systems include oroperate a plurality of after-treatment units wherein each of theplurality of units receives only part of an engine's exhaust stream. Forexample, an exemplary system includes one after-treatment unit forreceiving exhaust from two combustion chambers (e.g., cylinder, etc.)and another after-treatment unit for receiving exhaust from two othercombustion chambers wherein both after-treatment units treat the sameemission component or components. Of course, other exemplary systems mayinclude a one-to-one ratio of after-treatment units and enginecombustion chambers (e.g., a four cylinder engine may have an exemplarysystem that includes one after-treatment unit per cylinder). Yet anotherexemplary system includes a plurality of after-treatment units whereineach of the plurality of units is positioned prior to an exhaust turbineand receives only part of an engine's exhaust stream.

[0027]FIGS. 2, 3 and 4 show exemplary systems 200, 300, 400, which aresuitable for implementing various exemplary methods described herein.The exemplary systems 200, 300, 400 allow for after-treatmentregeneration of any particular after-treatment unit wherein a unitreceives only part of an engine's exhaust stream. In some instances,components of the exemplary systems 200, 300, 400 are optional. Forexample, as described in some exemplary methods, operation does notrequire an exhaust gas recirculation (EGR) system. Further, as describedin some exemplary methods, operation includes an exhaust turbine or aturbocharger and optionally a variable geometry mechanism or othermechanism for controlling exhaust flow to a turbine or turbines. Variousexemplary methods are presented after the description of the exemplarysystems 200, 300, 400.

[0028]FIG. 2 shows an exemplary system 200 that includes an exemplaryinternal combustion engine 210 and turbocharger 220. The internalcombustion engine 210 includes an engine block 218 housing a pluralityof combustion chambers (e.g., cylinders, etc.) that operatively drive ashaft 212. The turbocharger 220, which optionally includes a variablegeometry mechanism or electric generator and/or motor, compresses intakeair which circulates to an intake air heat exchanger 223 (e.g., to coolintake air, etc.).

[0029] As shown in FIG. 2, an intake system 214 provides a flow path forintake air to the engine block 218 while an exhaust system 216 providesa flow path for exhaust from the engine block 218. The exemplary system200 further includes a fuel system 208 that can route fuel to individualcombustion chambers and an exhaust gas recirculation (EGR) system 226that can route exhaust gas to the air intake system 214. The EGR system226 optionally includes an EGR flow regulator 230 and an EGR heatexchanger 234.

[0030] The air intake system 214 includes a plurality of flow regulators224, 224′, 224″, 224′″ that can regulate the flow of exhaust gas to eachcombustion chamber. Hence, the flow regulators 224, 224′, 224″, 224′″can regulate flow rates and regulate air to exhaust gas ratios to eachcombustion chamber. An alternative exemplary air intake system includesa plurality of flow regulators that can regulate air flow to eachcombustion chamber and that can regulate the flow of exhaust gas to eachcombustion chamber. Of course, yet other alternative exemplary airintake systems may have one or more flow regulators to allow forregulation of exhaust gas to one or more combustion chambers and otherregulators to allow for regulation of intake air (e.g., on achamber-by-chamber or any other particular basis). Intake air issupplied to the air intake system 214 via an air intake that optionallyincludes an intake flow regulator 221.

[0031] The exemplary exhaust system 216 allows for after-treatmentregeneration of any particular after-treatment unit wherein a unitreceives only part of an engine's exhaust stream. The exhaust system 216includes a plurality of after-treatment units 228, 228′, 228″, 228′″;wherein, each combustion chamber of the engine 210 has a respectiveexhaust stream directed to one of the after-treatment units 228, 228′,228″, 228′″. Exhaust passing through the after-treatment units 228,228′, 228″, 228′″ collects, for example, in a manifold to form anexhaust stream. The EGR system 226 branches off the exhaust stream,prior to any exhaust turbine, and can direct exhaust through the EGRheat exchanger 234 and then to the intake system 214.

[0032] Positioning of an after-treatment unit prior to a turbine can actto increase temperature of the after-treatment unit. Some units arequite temperature dependent, for example, catalytic units typicallyoperate more effectively at higher temperatures. Such units may benefitfrom such positioning. Further, after-treatment units for treatingexhaust from a single combustion chamber may be considerably smallerthan after-treatment units for treating exhaust from a plurality of suchcombustion chambers. In general, unit size and mass may decrease inrelation to the number of combustion chambers assigned to anafter-treatment unit. Hence, an exemplary after-treatment unit fortreating exhaust from a single combustion chamber has a smaller thermalmass than an after-treatment unit for treating exhaust from a pluralityof the combustion chambers. A smaller thermal mass typically equates toa smaller thermal inertia. Hence, such exemplary after-treatment unitscan allow for more dynamic and/or efficient control and/or operation.Further, a smaller sized unit may allow for a reduction in spatialvelocity when compared to a larger unit. Of course, the number ofcombustion chambers feeding an after-treatment unit and engineoperational parameters will also affect spatial velocity.

[0033]FIG. 3 shows an exemplary system 300 that includes an exemplaryinternal combustion engine 210. The internal combustion engine 210includes an engine block 218 housing a plurality of combustion chambers(e.g., cylinders, etc.) that operatively drive a shaft 212. As shown inFIG. 3, an intake system 214 provides a flow path for intake air to theengine block 218 while an exhaust system 316 provides a flow path forexhaust from the engine block 218. The exemplary system 300 furtherincludes a fuel system 208 that can route fuel to individual combustionchambers and an exhaust gas recirculation (EGR) system 226 that canroute exhaust gas to the air intake system 214. The EGR system 226optionally includes an EGR flow regulator 230 and an EGR heat exchanger234.

[0034] The air intake system 214 includes a plurality of flow regulators224, 224′, 224″, 224′″ that can regulate the flow of exhaust gas to eachcombustion chamber. Hence, the flow regulators 224, 224′, 224″, 224′″can regulate flow rates and regulate air to exhaust gas ratios to eachcombustion chamber. An alternative exemplary air intake system includesa plurality of flow regulators that can regulate air flow to eachcombustion chamber and that can regulate the flow of exhaust gas to eachcombustion chamber. Of course, yet other alternative exemplary airintake systems may have one or more flow regulators to allow forregulation of exhaust gas to one or more combustion chambers and otherregulators to allow for regulation of intake air (e.g., on achamber-by-chamber or any other particular basis).

[0035] Intake air is supplied to the air intake system 214 via an airintake that optionally includes an intake flow regulator 221. Further,intake air may be supplied to the air intake system 214 at an elevatedpressure (e.g., boost pressure) via a compressor or turbocharger.

[0036] The exemplary exhaust system 316 allows for after-treatmentregeneration of any particular after-treatment unit wherein a unitreceives only part of an engine's exhaust stream. The exhaust system 316includes a plurality of after-treatment units 228, 228′, 228″, 228′″;wherein, each combustion chamber of the engine 210 has a respectiveexhaust stream directed to one of the after-treatment units 228, 228′,228″, 228′″. The exemplary exhaust system 316 further includes aplurality of exhaust regulators 332, 332′, 332″, 332′″. Each of theexhaust regulators 332, 332′, 332″, 332′″ can regulate flow of exhaustfrom a respective after-treatment unit 228, 228′, 228″, 228′″. Whencompared to the exemplary exhaust system 216 of FIG. 2, the exemplaryexhaust system 316 allows for individual regulation of exhaust pressureand flow through each respective after-treatment unit.

[0037] Exhaust passing through the after-treatment units 228, 228′,228″, 228′″ and exhaust regulators 332, 332′, 332″, 332′″ collects, forexample, in a manifold to form an exhaust stream. Consequently, theexhaust regulators 332, 332′, 332″, 332′″ can to some degree regulate anindividual combustion chamber's contribution to the engine's exhaust.The EGR system 226 branches off the exhaust stream, prior to any exhaustturbine, and can direct exhaust through the EGR heat exchanger 234 andthen to the intake system 214.

[0038]FIG. 4 shows an exemplary system 400 that includes an exemplaryinternal combustion engine 210. The internal combustion engine 210includes an engine block 218 housing a plurality of combustion chambers(e.g., cylinders, etc.) that operatively drive a shaft 212. As shown inFIG. 4, an intake system 414 provides a flow path for intake air to theengine block 218 while an exhaust system 316 provides a flow path forexhaust from the engine block 218. The exemplary system 400 furtherincludes a fuel system 208 that can route fuel to individual combustionchambers and an exhaust gas recirculation (EGR) system 226 that canroute exhaust gas to the air intake system 214. The EGR system 226optionally includes an EGR flow regulator 230 and an EGR heat exchanger234.

[0039] The air intake system 414 includes a plurality of flow regulators425, 425′, 425″, 425′″ that can regulate flow of intake air to eachcombustion chamber. Hence, the flow regulators 425, 425′, 425″, 425′″can regulate flow rates to each combustion chamber. Intake air issupplied to the air intake system 414 via an air intake that optionallyincludes an intake flow regulator 221. Further, intake air may besupplied to the air intake system 414 at an elevated pressure (e.g.,boost pressure) via a compressor or turbocharger. When compared to theexemplary air intake systems 214 of FIG. 2 and 314 of FIG. 3, theexemplary intake system 414, where appropriate, relies on exhaust gasrecirculation regulated via a common regulator that routes exhaust gasto an air intake manifold.

[0040] The exemplary exhaust system 316 allows for after-treatmentregeneration of any particular after-treatment unit wherein a unitreceives only part of an engine's exhaust stream. The exhaust system 316includes a plurality of after-treatment units 228, 228′, 228″, 228′″;wherein, each combustion chamber of the engine 210 has a respectiveexhaust stream directed to one of the after-treatment units 228, 228′,228″, 228′″. The exemplary exhaust system 316 further includes aplurality of exhaust regulators 332, 332′, 332″, 332′″. Each of theexhaust regulators 332, 332′, 332″, 332′″ can regulate flow of exhaustfrom a respective after-treatment unit 228, 228′, 228″, 228′″. Whencompared to the exemplary exhaust system 216 of FIG. 2, the exemplaryexhaust system 316 allows for individual regulation of exhaust pressureand flow through each respective after-treatment unit.

[0041] Exhaust passing through the after-treatment units 228, 228′,228″, 228′″ and exhaust regulators 332, 332′, 332″, 332′″ collects, forexample, in a manifold to form an exhaust stream. Consequently, theexhaust regulators 332, 332′, 332″, 332′″ can to some degree regulate anindividual combustion chamber's contribution to the engine's exhaust.The EGR system 226 branches off the exhaust stream, prior to any exhaustturbine, and can direct exhaust through the EGR heat exchanger 234 andthen to the intake system 214.

[0042]FIG. 5 shows an exemplary method 500 for regenerating anafter-treatment unit. The method 500 commences in a selection block 504wherein an after-treatment unit is selected for regeneration. Adetermination block 508 follows that determines one or more parametervalues. For example, a determination block may determine an appropriateair to fuel ratio for regenerating the selected after-treatment unit. Anair to fuel ratio is optionally a pre-combustion air to fuel ratio or apost-combustion air to fuel ratio. An adjustment block 512 allows foradjusting one or more regulators in a manner suitable to achieve thedesired parameter value(s) (e.g., to achieve a desired air to fuelratio, etc.). A regeneration block 516 follows wherein regeneration ofthe selected after-treatment unit occurs. The exemplary method 500optionally repeats, as desired, for a series of after-treatment units.For example, if an engine has four cylinders and an after-treatment unitfor each cylinder, the selection may repeat according to a firing order(e.g., 1-3-2-4, etc.) or some other order. In general, regeneration ofan after-treatment unit occurs at a frequency less than the firingfrequency of a chamber. Further, an exemplary method may select morethan one after-treatment unit and adjust parameters for associatedcombustion chambers. Yet further, an exemplary method may select anafter-treatment unit having a plurality of associated combustionchambers wherein the number of associated combustion chambers istypically less than the total number of combustion chambers for theengine.

[0043] With reference to the exemplary systems 200, 300, 400 of FIGS. 2,3, and 4, the selection block 504 may select an after-treatment unitfrom the after-treatment units 228, 228′, 228″, 228′″. In the exemplarysystem 200, the adjustment block 512 may adjust any of the variousregulators to achieve one or more parameter values, such as, a desiredair to fuel ratio, etc. For example, the adjustment block 512 may adjustregulators associated with the fuel system 208, the EGR system 238,and/or the air intake system 214. Exemplary adjustment parameters thatmay be individually and directly adjustable for each combustion chamberinclude, but are not limited to, intake air pressure, intake air flow,EGR pressure, EGR flow, fuel flow, and fuel pressure. Further, if theexemplary system 200 includes a variable geometry turbine, then theadjustment block 512 may adjust the geometry to thereby affect exhaustpressure and flow. In turn, an adjustment to a variable geometry turbinemay affect EGR pressure and flow. Further, an adjustment to a variablegeometry turbine may affect operation of an associated compressor (e.g.,as part of a turbocharger), which, in turn, may affect pressure and flowof intake air.

[0044] With respect to the exemplary system 300 of FIG. 3, theadjustment block 512 may adjust any of the various regulators to achieveone or more parameter values, such as, a desired air to fuel ratio, etc.For example, the adjustment block 512 may adjust regulators associatedwith the fuel system 208, the EGR system 238, the air intake system 214and/or the exhaust system 316. Exemplary adjustment parameters that maybe individually and directly adjustable for each combustion chamberinclude, but are not limited to, intake air pressure, intake air flow,EGR pressure, EGR flow, exhaust flow, exhaust pressure, fuel flow, andfuel pressure. Further, if the exemplary system 300 includes a variablegeometry turbine, then the adjustment block 512 may adjust the geometryto thereby affect exhaust pressure and flow. In turn, an adjustment to avariable geometry turbine may affect EGR pressure and flow. Further, anadjustment to a variable geometry turbine may affect operation of anassociated compressor (e.g., as part of a turbocharger), which, in turn,may affect pressure and flow of intake air.

[0045] With respect to the exemplary system 400 of FIG. 4, theadjustment block 512 may adjust any of the various regulators to achieveone or more parameter values, such as, a desired air to fuel ratio, etc.For example, the adjustment block 512 may adjust regulators associatedwith the fuel system 208, the EGR system 238, the air intake system 414and/or the exhaust system 316. Exemplary adjustment parameters that maybe individually and directly adjustable for each combustion chamberinclude, but are not limited to, intake air pressure, intake air flow,exhaust flow, exhaust pressure, fuel flow, and fuel pressure. Further,if the exemplary system 300 includes a variable geometry turbine, thenthe adjustment block 512 may adjust the geometry to thereby affectexhaust pressure and flow. In turn, an adjustment to a variable geometryturbine may affect EGR pressure and flow. Further, an adjustment to avariable geometry turbine may affect operation of an associatedcompressor (e.g., as part of a turbocharger), which, in turn, may affectpressure and flow of intake air.

[0046]FIG. 6 shows a plot 600 of exemplary trends for hydrocarbonconcentration and smoke versus air to fuel ratio. Such trends have beenshown to exist for low temperature combustion (LTC) operation in dieselengines. According to one LTC scheme, a relatively high EGR flow isintroduced into an intake manifold that feeds a plurality of combustionchambers (see, e.g., arrow for direction of increasing EGR with respectto intake air). Such a scheme is described in Akihama, et al.,“Mechanism of the Smokeless Rich Diesel Combustion by ReducingTemperature”, SAE 2001 World Congress (No. 2001-01-0655), March 2001(Detroit, Mich.), which is incorporated by reference herein. In this LTCscheme, the relatively high EGR flow acts to reduce temperature andoxygen concentration of intake air directed to the plurality ofcombustion chambers. Use of an EGR cooler may allow for cooling ofrecirculated exhaust gas. Trends exhibited by such a LTC scheme includean increase in hydrocarbon concentration (e.g., a “rich spike”, etc.)and a decrease in smoke (e.g., soot, etc.) as air to fuel ratioapproaches a stoichiometric ratio (e.g., as the air to fuel ratiobecomes less than some critical ratio). Yet further, such a LTC schemecan reduce NOx emissions from the combustion chambers.

[0047] The generation of a “rich spike” can aid regeneration of someafter-treatment units. For example, the hydrocarbons associated with the“rich spike” can be carried by the exhaust to a NOx after-treatmentunit. Once in the NOx after-treatment unit, the hydrocarbons can react(e.g., oxidize, etc.) and release heat. The released heat can increasetemperature of the NOx unit and thereby facilitate regeneration.However, according to conventional LTC schemes, “rich spike” generationcan cause a decrease in engine power or other performance glitch.

[0048] An exemplary method aims to reduce, minimize and/or eliminateissues associated with conventional LTC schemes by generating a richspike that is limited to less than all of an engine's combustionchambers. For example, an exemplary method generates a rich spike on acombustion chamber by combustion chamber basis. FIG. 7 shows a plot 700of NOx concentration and after-treatment unit temperature correspondingto such an exemplary method. More specifically, the plot 700 shows NOxdata for a first combustion chamber (e.g., cylinder n_(i), cylinder 1 of4, etc.) and NOx data for a second combustion chamber (e.g., cylindern_(i+1), cylinder 3 of 4, etc.) wherein rich spike generation on acombustion chamber by combustion chamber basis causes periodicreductions in NOx emissions. Further, rich spike generation on acombustion chamber by combustion chamber basis causes periodictemperature increases in one or more associated after-treatment units.Again, an increase in temperature can be part of and/or facilitateafter-treatment unit regeneration.

[0049]FIG. 8 shows an exemplary plot 800 of power versus time for anexemplary method and a conventional method of after-treatmentregeneration. The exemplary method corresponds to combustion chamber bycombustion chamber rich spike generation and/or low temperaturecombustion; whereas, the conventional method corresponds to rich spikegeneration and/or low temperature combustion for all combustion chambersin a substantially simultaneous manner. For example, the exemplarymethod may be implemented on a four cylinder engine having a firingorder or 1-3-4-2 wherein rich spike generation and/or low temperaturecombustion occurs first for cylinder 1, then for cylinder 3, then forcylinder 4, and then for cylinder 2. In contrast, the conventionalmethod would result in substantially simultaneous rich spike generationand/or low temperature combustion for all the cylinders 1, 2, 3 and 4.

[0050] According to the exemplary method, a combustion chamber isselected for rich spike generation and/or low temperature combustion.Next, one or more regulators are adjusted to generate a rich spikeand/or to achieve low temperature combustion for the selected combustionchamber. The overall effect of this exemplary method is to reduce themagnitude of power transients. For example, the exemplary methodproduces smaller power transients than the conventional method. Whilethe conventional method may produce fewer power transients (e.g., lesserfrequency), the exemplary method reduces the magnitude of the powertransients, which acts to minimize the affect of any particulartransient on performance. Of course, such an exemplary method may selectmore than one combustion chamber and less than all the combustionchambers. Alternatively, such an exemplary method may select less thanall after-treatment units and then associate the selected units withless than all combustion chambers.

[0051] Further, various exemplary methods and/or systems can controlexhaust flow through an after-treatment unit. For example, a reductionin space velocity during regeneration may help to minimize any fueleconomy penalty associated with operation of the after-treatment unit.Further, control of various adjustment parameters may allow for adecrease in oxygen concentration in an exhaust stream to a NOxafter-treatment unit to thereby help create a reducing environment tofacilitate regeneration of the NOx after-treatment unit. In this manner,hydrocarbons are less likely to react with oxygen prior to reaction inan after-treatment unit. More specifically, after-treatment units forNOx typically operate according to a sorption and regeneration cycle.During a sorption phase, NOx sorption occurs in an oxidative environment(e.g., sufficient exhaust oxygen and little exhaust hydrocarbon, i.e.,lean); whereas, during a regeneration phase, adsorbed NOx is releasedand/or reduced to N₂ in a reducing environment (e.g., little or noexhaust oxygen and sufficient exhaust hydrocarbon, i.e., rich). Overall,the following simplified equations (e.g., stoichiometric amounts notindicated) may exemplify a sorption and regeneration cycle: Sorption:NO + O₂ → adsorbed NO₃ Regeneration: Adsorbed NO₃ + HC → N₂ + H₂O

[0052] Again, while some exhaust oxygen may be present during aregeneration phase, the concentration of such exhaust oxygen istypically significantly less than in a sorption phase. Hence, variousexemplary methods aim to periodically increase hydrocarbon (HC)concentration to one or more after-treatment units and/or to decreaseoxygen concentration to the one or more after-treatment units. Ingeneral, such an exemplary method increases HC concentration and/ordecreases oxygen concentration to one or more after-treatment unit byregulating parameters associated one or more combustion chambers whereinthe one or more combustion chambers number less than all of thecombustion chambers. As described below, such exemplary methods and/orother exemplary methods may regulate parameters associated with othercombustion chambers to achieve or maintain certain engine operatingconditions.

[0053]FIG. 9 shows an exemplary plot 900 of engine power versus time foran exemplary method. The plot 900 includes expected power transients andcompensation power transients that result in a total power. In thisparticular example, the total power remains substantially constant withrespect to time. Of course, total power could vary based on operatingconditions (e.g., operator demand, etc.). More specifically, the plot900 shows expected power transients for a four cylinder engine having afiring order 1-3-4-2 (see, e.g., the plot 800 of FIG. 8). To compensatefor the expected power transients, an exemplary method increases powergenerated by one or more of the other cylinders. For example, ifparameters associated with cylinder 1 are adjusted to generate a richspike, then parameters for one or more of cylinders 2, 3 and 4 may beadjusted to compensate for cylinder 1's expected power transient.Conventional schemes that rely on all of an engine's cylinders togenerate a rich spike substantially simultaneously cannot effectivelycompensate for the resulting power transient in this manner. Such anexemplary method may also control a turbine, a compressor or aturbocharger to compensate (e.g., as an alternative or in addition tocontrol of other currently “non-regenerative” chambers).

[0054]FIG. 10 shows a block diagram of an exemplary method 1000 forregenerating one or more after-treatment units. In a selection block1004, one or more after-treatment units are selected for regeneration. Adetermination block 1008 follows that determines which parametersrequire adjustment and/or determines values for one or more of theparameters. In this block, the exemplary method 1000 may determine avalue for a parameter associated with a certain combustion chamber togenerate a rich spike while also determining a value for a parameterassociated with another combustion chamber to compensate for an expectedpower transient. Various adjustment blocks 1012, 1014 follow whichadjust regulators according to one or more parameter values. Forexample, a first set of parameter values may be used to adjust one ormore regulators associated with a combustion chamber and a correspondingafter-treatment unit while a second set of parameter values may be usedto adjust one or more regulators associated with one or more othercombustion chambers and/or other after-treatment units. The exemplarymethod 1000 continues in a regeneration block 1016 wherein the one ormore selected after-treatment units experiences conditions favorable toregeneration (e.g., increase in HC, decrease in oxygen, etc.).

[0055] The exemplary method 1000 is suitable for implementation using acontroller. For example, in an engine system (e.g., exemplary enginesystems 200, 300, 400, etc.) that includes a plurality of combustionchambers and a plurality of after-treatment units, an exemplarycontroller can selectively control air to fuel ratio to less than all ofthe combustion chambers to thereby selectively cause less than all ofthe after-treatment units to receive exhaust having hydrocarbon andoxygen concentrations that favor after-treatment unit regeneration. Forexample, a V6 engine may have a first after-treatment unit for a firstbank of three cylinders and a second after-treatment unit for a secondbank of three cylinders. According to such an exemplary method, acontroller may selectively control air to fuel ratio to the first bankof three cylinders to thereby selectively cause the firstafter-treatment unit to receive exhaust having hydrocarbon and oxygenconcentrations that favor after-treatment unit regeneration (e.g.,typically an increased hydrocarbon concentration and a decreased oxygenconcentration). Thus, in the example of the V6 engine, an engine hasmore than one group of combustion chambers wherein each group has anassociated after-treatment unit. Of course, as mentioned previously,each combustion chamber may have an associated after-treatment unit.

[0056] Another exemplary method includes injecting fuel into an exhauststream associated with less than all combustion chambers of an engine,typically via an exhaust fuel regulator positioned on an exhaust outletof a combustion chamber. Any exemplary engine system (see, e.g., thesystems 200, 300, 400, etc.) may have a plurality of such exhaust fuelregulators to inject fuel into an associated exhaust stream (e.g., on acombustion chamber by combustion chamber basis or other basis).Conventionally, an exhaust fuel regulator to inject fuel into an exhaustmanifold has been part of an exhaust port injection scheme that canincrease hydrocarbon concentration in an exhaust manifold. In contrast,an exemplary method uses a plurality of exhaust fuel regulators toadjust hydrocarbon concentration in a plurality of exhaust streams. Forexample, such an exemplary method may adjust the flow of exhaust fuel toless than all of the exhaust streams and then adjust the flow of exhaustfuel to other of the exhaust streams. In a V6 engine, such an exemplarymethod may operate to adjust the flow of exhaust fuel to a first exhaustmanifold that collects exhaust from three combustion chambers anddirects the collected exhaust to a first after-treatment unit and thenadjust the flow of exhaust fuel to a second exhaust manifold thatcollects exhaust from three other combustion chambers and directs thecollected exhaust to a second after-treatment unit. In this manner,regeneration of the first after-treatment unit and the secondafter-treatment unit may be controlled independently.

[0057] Various exemplary methods that include post-combustion chamberinjection of fuel to an exhaust stream may augment various other methodsdescribed herein. For example, a decrease in exhaust oxygenconcentration may occur via an EGR control while an increase inhydrocarbon concentration may occur via an exhaust fuel regulator. Forexample, an engine system that includes a plurality of combustionchambers, each having an associated EGR regulator, may implement anexemplary method that increases EGR on a combustion chamber bycombustion chamber basis. In this example, each EGR increase may becoordinated with injection of fuel into a corresponding exhaust streamof a combustion chamber. Such an exemplary method may also be beneficialto augment a rich spike and thereby further increase exhaust hydrocarbonconcentration.

[0058]FIG. 11 shows an exemplary system 1100 that includes an exemplarycontroller 1110 for adjusting various regulators. Note, that for ease ofdescription, not all of the combustion chambers or regulators are shownin FIG. 11. The exemplary system 1100 includes a plurality of combustionchambers, such as, cylinder n_(i) of n_(T), where n_(T) is the totalnumber of cylinders. The cylinder n_(i) has associated regulators, suchas, an air intake/EGR regulator 224, an exhaust regulator 332, an intakefuel regulator 207, and an exhaust fuel regulator 209. While the intakefuel regulator 207 (an engine system typically has a plurality, e.g.,one per combustion chamber) regulates fuel to the cylinder n_(i), theexhaust fuel regulator 209 regulates fuel to an exhaust. Any exemplaryengine system (see, e.g., the systems 200, 300, 400, etc.) may have aplurality of such exhaust fuel regulators to inject fuel into an exhauststream.

[0059] The exemplary system 1100 also includes various system regulators(e.g., air intake regulator 221, EGR regulator 230, etc.). Further, theexemplary system 1100 includes a controller for controlling a variousaspects of a turbine, a compressor, or a turbocharger (e.g., variablegeometry or other). Of course, other engine control systems and/orassociated equipment may be used to implement various exemplary methodspresented herein. For example, valves and valve timing are optionallyused to adjust air to fuel ratio, EGR, exhaust, etc. or as adjustmentparameters.

[0060] The exemplary controller 1110 includes an air module 1114 forcontrolling intake air pressure and/or flow to the chamber n_(i), a fuelmodule 1118 for controlling fuel pressure and/or flow to the chambern_(i) (and optionally fuel pressure and/or flow to an exhaust of thecylinder n_(i)), an exhaust module 1122 for controlling exhaust pressureand/or flow from the chamber n_(i), and an EGR module 1126 forcontrolling pressure and/or flow of EGR to the chamber n_(i). Of course,the exemplary controller 1110 may include other modules for controllingvarious parameters germane to operation of an engine or engine system.

[0061] The exemplary controller 1110 typically includes control logicfor selectively controlling air to fuel ratio to less than all of thecombustion chambers to thereby selectively cause less than all of theafter-treatment units to receive exhaust having hydrocarbon and oxygenconcentrations that favor after-treatment unit regeneration. Such logicmay depend on other engine system parameters, such as, but not limitedto, demand, engine speed, load, type and number of after-treatmentunits, fuel quality, air quality, altitude, etc. Exemplary control logicschedules regeneration for a plurality of after-treatment units.Further, exemplary control logic may compensate for any expecteddecrease in engine performance associated with such a schedule and/orother engine operating conditions.

[0062] Various exemplary methods, devices and/or systems allow forregeneration of after-treatment units on a combustion chamber bycombustion chamber basis wherein each combustion chamber has anassociated after-treatment unit. Accordingly, the impact of regenerationon an engine may be reduced by a factor equal to the number ofcombustion chambers. As an example, regenerating a NOx unit (e.g., atrap, etc.) may require reducing mass flow to one cylinder by a factorof two, which impacts total mass flow by 8% on a 6 cylinder engine, incontrast to reducing mass flow by a factor of 50% for regeneration of aNOx unit that handles emissions from all cylinders. Other exemplarymethods, device and/or systems allow for regeneration of anafter-treatment unit by controlling parameters associated with less thanall combustion chambers of an engine.

[0063] An exemplary system and/or method may accomplish such a reducedimpact by including one or more valves in an intake manifold or an airintake system (e.g., exemplary air intake systems 214, 414) or throughuse of variable valve timing on an engine. According to variousexemplary methods, oxygen flow can be reduced through any particularcombustion chamber, the fuel flow increased, or the two combined toachieve a rich condition (e.g., a rich spike, etc.) suitable for NOxafter-treatment unit regeneration. Various exemplary methods aresuitable for use to increase temperature of a diesel particulate filterand thus cause regeneration of such an after-treatment unit.

[0064] Further, according to various exemplary methods and/or systems,after-treatment units are positioned prior to any exhaust turbine tothereby allow the units to be exposed to higher exhaust temperatures,which can result in a need for a lesser change in air to fuel ratio toachieve regeneration and optionally an increase in economy (e.g., fueleconomy, etc.). Yet further, various exemplary methods and/or systemsmitigate changes in combustion chamber conditions at or near the pointof after-treatment unit regeneration and hence have less affect onexhaust turbine performance when compared to a conventionalafter-treatment unit positioned after an exhaust turbine.

[0065] While various exemplary systems and/or methods are shownindividually in various figures, yet other exemplary systems and/ormethod optionally implement a combination of features. Although someexemplary methods, devices and systems have been illustrated in theaccompanying Drawings and described in the foregoing DetailedDescription, it will be understood that the methods and systems are notlimited to the exemplary methods, devices and/or systems disclosed, butare capable of numerous rearrangements, modifications and substitutionswithout departing from the spirit set forth and defined by the followingclaims.

What is claimed is:
 1. An engine system comprising: a plurality ofcombustion chambers; a plurality of after-treatment units; a controllerto selectively control air to fuel ratio to less than all of thecombustion chambers to thereby selectively cause less than all of theafter-treatment units to receive exhaust having hydrocarbon and oxygenconcentrations that favor after-treatment unit regeneration.
 2. Theengine system of claim 1 wherein the plurality of combustion chambersinclude diesel fuel combustion chambers.
 3. The engine system of claim 1wherein the plurality of after-treatment units include NOxafter-treatment units.
 4. The engine system of claim 1 wherein each ofthe plurality of after-treatment units is configured to receive exhaustfrom one of the plurality of combustion chambers.
 5. The engine systemof claim 1 wherein each of the plurality of after-treatment units ispositioned prior to an exhaust turbine.
 6. The engine system of claim 1further comprising a plurality of regulators to regulate exhaust gasrecirculation to the plurality of combustion chambers.
 7. The enginesystem of claim 6 wherein the plurality of regulators allow forindependent regulation of exhaust gas recirculation to each of theplurality of combustion chambers.
 8. A controller for use with an enginesystem having a plurality of combustion chambers and a plurality ofafter-treatment units comprising: control logic for selectivelycontrolling air to fuel ratio to less than all of the combustionchambers to thereby selectively cause less than all of theafter-treatment units to receive exhaust having hydrocarbon and oxygenconcentrations that favor after-treatment unit regeneration.
 9. Thecontroller of claim 8, wherein the control logic includes a schedule forregenerating the plurality of after-treatment units.
 10. The controllerof claim 9 wherein the schedule depends on engine operating conditions.11. The controller of claim 8 wherein the hydrogen and oxygenconcentrations favor regeneration of a NOx after-treatment unit.
 12. Amethod of operating an engine system comprising: selecting less than allof a plurality of after-treatment units; and adjusting air to fuel ratiofor less than all of a plurality of combustion chambers to thereby causethe selected after-treatment units to receive exhaust having hydrocarbonand oxygen concentrations that favor regeneration of the selectedafter-treatment units.
 13. The method of claim 12 wherein thehydrocarbon and oxygen concentrations favor regeneration of a NOxafter-treatment unit.
 14. The method of claim 12 wherein the adjustingincreases hydrocarbon concentration.
 15. The method of claim 12 whereinthe adjusting decreases oxygen concentration.
 16. The method of claim 12wherein the adjusting increases hydrocarbon concentration and decreasesoxygen concentration.
 17. The method of claim 12 wherein the adjustingadjusts exhaust gas recirculation.
 18. The method of claim 17 whereinthe adjusting adjusts exhaust gas recirculation on a combustion chamberby combustion chamber basis.
 19. The method of claim 12 furthercomprising compensating for any expected performance detriment caused bythe adjusting.
 20. The method of claim 19 wherein the compensatingincludes adjusting operational parameters for other of the plurality ofcombustion chambers.
 21. The method of claim 12 wherein the selectingselects one of the after-treatment units and the adjusting adjusts anair to fuel ratio for one of the plurality of combustion chambers. 22.The method of claim 12 wherein the adjusting adjusts parameters forother of the plurality of combustion chambers.
 23. One or morecomputer-readable media having instructions thereon that are executableby a computer to perform actions comprising: adjusting air to fuel ratiofor less than all of a plurality of combustion chambers to thereby causeless than all of a plurality of after-treatment units to receive exhausthaving hydrocarbon and oxygen concentrations that favor regeneration ofthe less than all after-treatment units.
 24. A controller comprising:means for adjusting air to fuel ratio for less than all of a pluralityof combustion chambers to thereby cause less than all of a plurality ofafter-treatment units to receive exhaust having hydrocarbon and oxygenconcentrations that favor regeneration of the less than allafter-treatment units.